1. Field of the Invention
The present invention relates to an ultrathin-walled rolling bearing used, for example, in industrial robots, machine tools, medical instruments, and the like, and it also relates to a cage incorporated in such bearings.
2. Description of the Prior Art
FIG. 14 shows an example of a CT scanner device that is a kind of medical instrument. As shown in the same figure, in the CT scanner device, X-rays produced by an X-ray tube device 1 are radiated to a subject 4 through a wedge filter 2 for uniformizing their intensity distribution and a slit 3 for restricting said intensity distribution. The X-rays passing through the subject 4 are received by a detector 5, where they are converted into an electric signal, which is then fed to an unillustrated computer.
Such parts as the X-ray tube device 1, wedge filter 2, slit 3, and detector 5 in this CT scanner device are mounted on a substantially cylindrical rotary frame 8 rotatably supported on a fixed frame 7 through a bearing 6, the rotary driving of said rotary frame 8 rotating the parts around the subject 4. In the CT scanner device, the rotary motion of the mutually opposed X-ray tube device 1 and detector 5 around the subject 4 provides the projection data covering all angles in the examination cross-section of the subject 4, and a tomographic image is obtained from a reconstructed program programmed in advance from these data.
In the CT scanner device, since the inner periphery of the fixed frame 7 is formed with a large diameter (about 1 m) to receive the subject 4, a bearing that is very small in cross-sectional area for its diameter, or a so-called ultrathin-walled rolling bearing is used as the bearing 6 between the fixed and rotary frames 7 and 8.
In the prior art, for ultrathin-walled rolling bearings used in CT scanner devices, split type cages are frequently used. Such type of cage 11 is of split construction, as shown in FIGS. 15 and 17, having a plurality of arcuate segments 12 annularly formed by being circumferentially joined together. In the prior art, as shown in FIGS. 17(a) and (b) and 18(a) and (b), each segment 12 is formed at its opposite ends with projection-shaped or recess-shaped fitting sections 13 and 14, and such projection-shaped or recess-shaped fitting sections 13 and 14 are assembled, by fitting, to the recess-shaped or projection-shaped fitting sections 14 and 13 at the ends of the mating segment (see FIG. 19). That is, as shown in FIG. 20, one (for example, projection-shaped) fitting section 13 of the segment 12 is radially pushed into the recess-shaped fitting section 14 of the mating segment 12, whereby they are circumferentially engaged with each other to form a cage 11 (see, for example, Japanese Unexamined Patent Publications 2001-304266 (paragraph no. 0018, and FIGS. 2 and 3) and 2002-81442 (paragraph no. 0016, and FIGS. 3 and 4). Each segment 12 is formed with a pocket 15 for receiving a ball.
In this connection, in the prior art, a proper interference is imparted to the fitting sections 13 and 14 of the segments 12 constituting the cage 11 and the mating segments 12 are joined, thereby forming an annular cage 11. The segments 12 forming this cage 11 are generally injection moldings of resin, with the result that molding errors or the like causes the interference between the fitting sections to increase in some cases or decrease in other cases, sometimes resulting in rattling produced between the fitting sections 13 and 14.
If the interference between the fitting sections 13 and 14 of the segments 12 increases as described above, the two fitting sections 13 and 14 tend to easily interfere with each other when one fitting section 13 is radially pushed into the mating fitting section 14, so that smooth fitting of the two fitting sections 13 and 14 becomes difficult and the operating efficiency greatly lowers.
Reversely, if the interference between the fitting sections 13 and 14 of the segments 12 decreases to produce rattling, the cage 11 tends to easily change in shape from a right circle to a polygon, producing a radially inward or outward deviation between the adjacent segments 12, the deviated segment 12 coming into contact with the raceway surface of the inner or outer member, generating abnormal sounds such as hammering sounds or vibrating sounds, and causing a rise in bearing torque.
Particularly in the CT scanner device, abnormal sounds of this type are likely to induce a stress in the subject 4, making it strongly desired to lower the abnormal sound generating level Further, in the case where the rolling elements in the cage 11 are balls, a decrease in the clearance between the pocket 15 and the balls due to contraction deformation of the pocket 15 tends to restrain the balls in the pockets 15, resulting in an increase in the bearing torque.
The present invention has for its object the provision of a cage adapted to suppress rattling in fitted-together segments and to improve operating efficiency in joining segments, and an ultrathin-walled rolling bearing having such cage.
The invention provides a cage composed of a plurality of arcuate segments, wherein the joining projection formed in the bonding section of one of adjacent segments is fitted in a joining recess formed in the bonding section of the other segment to thereby annularly bond the segments, said cage being characterized in that said joining projections and joining recesses have a tapered fitting surface, for example, a conical surface, as seen in a radial section, and joining is effected by closely contacting the two fitting surfaces. In addition, the radial dimension of the jointing projections and joining recesses may be made smaller than the radial dimension of the segments. Here, the above-mentioned xe2x80x9cradialxe2x80x9d means radial with respect to a circle defined by the segments when annularly bonded together.
In the cage of the invention, fitting the bonding sections of the segments along the radially tapered fitting surfaces, for example, conical surfaces, allows a change in interference between the joining projections and recesses due to molding errors or the like to escape radially of the cage in the fitting surfaces, so that rattling in the fitted state can be suppressed to realize a stabilized fitted state. Therefore, the function of the cage can be maintained stabilized for a long time, and the generation of abnormal sounds due to contact between radially deviated segments and the raceway surfaces of the inner and outer members can be reliably prevented. Assembly of the cage can be easily effected, efficient assembly being possible. It is desired that the segments constituting the cage of the invention be made of resin, such as PPS (polyphenylene sulfide).
In the above arrangement, the butt surface of the bonding section of one of adjacent segments is formed with a projecting engaging section while the butt surface of the bonding section of the other segment is formed with a recessed engaging section, and the two butt surfaces butt against each other; thus radial positional deviation of the cage can be reliably prevented by controlling the radial position of the segments; this serves as a slip-off prevention means.
A cage which is a target of the invention is annularly formed by circumferentially bonding a plurality of segments, has pockets for receiving rolling elements at circumferentially equispaced intervals, and is suitable for use in an ultrathin-walled rolling bearing whose ratio of the diameter of said rolling elements to the pitch circle diameter of the bearing is not more than 0.03.
The cage of said arrangement is adapted to constitute an ultrathin-walled rolling bearing by combining an outer member having a raceway surface in its inner periphery, an inner member having a raceway surface in its outer-periphery, and a plurality of rolling elements interposed between the raceway surfaces of said outer and inner members, and in this ultrathin-walled rolling bearing, the cage having the rolling elements circumferentially equispaced therein is capable of reliably preventing the generation of abnormal sounds due to contact between the segments and the raceway surfaces of the inner and outer members.
If one of the outer and inner members in this ultrathin-walled rolling bearing is fixed in the rotary frame of a CT scanner device rotating around a subject and the other is fixed in the fixed frame of the CT scanner device, then it is possible to provide a CT scanner device which has low noise and is superior in radiographic accuracy.